TN and STN liquid-crystal display

ABSTRACT

TN liquid-crystal displays and supertwist liquid-crystal displays (SLCDs) having very short response times and good steepnesses and angle dependencies are obtained by using nematic liquid-crystal mixtures which comprise at least one compound of formula IA ##STR1## and at least one compound of the formula IB ##STR2## in which R a , R b , R c , L and r are as defined herein.

The invention relates to TN liquid-crystal displays and supertwistliquid-crystal displays (SLCDs) having very short response times andgood steepnesses and angle dependencies, and to the nematicliquid-crystal mixtures according to the invention used therein.

SLCDs as defined in the preamble are known, for example from EP 0 131216 B1; DE 34 23 993 A1; EP 0 098 070 A2; M. Schadt and F. Leenhouts,17th Freiburg Congress on Liquid Crystals (8.-10.04.87); K. Kawasaki etal., SID 87 Digest 391 (20.6); M. Schadt and F. Leenhouts, SID 87 Digest372 (20.1); K. Katoh et al., Japanese Journal of Applied Physics, Vol.26, No. 11, L 1784-L 1786 (1987); F. Leenhouts et al., Appl. Phys. Lett.50 (21), 1468 (1987); H. A. van Sprang and H. G. Koopman, J. Appl. Phys.62 (5), 1734 (1987); T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45(10), 1021 (1984), M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (5),236 (1987) and E. P. Raynes, Mol. Cryst. Liq. Cryst. Letters Vol. 4 (1),pp. 1-8 (1986). The term SLCD here covers any more highly twisteddisplay element with a value for the twist angle of between 160° and360°, such as, for example, the display elements of Waters et al. (C. M.Waters et al., Proc. Soc. Inf. Disp. (New York) (1985) (3rd Intern.Display Conference, Kobe, Japan), STN-LCDs (DE-A 35 03 259), SBE-LCDs(T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (1984) 1021),OMI-LCDs (M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (1987), 236,DST-LCDs (EP-A 0 246 842) or BW-STN-LCDs (K. Kawasaki et al., SID 87Digest 391 (20.6)).

SLCDs of this type are distinguished, in comparison to standard TNdisplays, by significantly better steepnesses of the electroopticalcharacteristic line and consequently better contrast values, and bysignificantly less angle dependence of the contrast. Of particularinterest are SLCDs having very short response times, in particular alsoat relatively low temperatures. In order to achieve short responsetimes, the viscosities, in particular, of the liquid-crystal mixtureswere hitherto optimized using usually monotropic additives havingrelatively high vapour pressure. However, the response times achievedwere not adequate for all applications.

In order to achieve a steep electrooptical characteristic line in SLCDs,the liquid-crystal mixtures should have relatively large values for K₃/K₁ and relatively small values for Δε/ε.sub.⊥.

In addition to optimization of the contrast and the response times,further important requirements are made of mixtures of this type:

1. A broad d/p window

2. High long-term chemical stability

3. High electrical resistance

4. Low frequency dependence of the threshold voltage.

The parameter combinations achieved are still far from adequate, inparticular for high-multiplex STNs (1/400). This is in some casesattributable to the fact that the various requirements are affected inopposite manners by material parameters.

There thus continues to be a great demand for TN and STN displays, inparticular for high-resolution displays (XGA), having very shortresponse times and at the same time a large operating temperature range,high characteristic line steepness, good angle dependence of thecontrast and low threshold voltage which meet the abovementionedrequirements.

An object of the invention is to provide liquid-crystal displays whichdo not have the above-mentioned disadvantages, or only do so to a lesserextent, and at the same time have very good response times and very goodsteepnesses.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

It has now been found that these objects can be achieved if nematicliquid-crystal mixtures are used which comprise compounds of the formulaIB ##STR3## in combination with esters of the formula IA ##STR4## inwhich R^(a) is an alkyl group having 1 to 12 carbon atoms, in which, inaddition, one or two non-adjacent CH₂ groups may be replaced by --O--,--CH═CH--, --CO--, --OCO-- or --COO--,

R^(b) and R^(c) are each, independently of one another, an alkenyl grouphaving 2 to 7 carbon atoms,

L is H or F, and

r is 0 or 1.

The use of compounds of the formulae IA and IB in TN and STN mixturesproduces

low viscosity and low temperature dependence of the viscosity

long shelf lives in the display at low temperatures,

very low S→N transitions, and

very fast response times, in particular at low temperatures.

The compounds of the formulae IA and IB significantly shorten theresponse times of TN and STN mixtures without impairing the steepnesses.

In particular, the compounds of the formula IB produce

a significant shortening of the response times while at the same timeincreasing the steepness, and

an increase in the clearing temperatures without impairing the responsetimes.

The invention thus relates to a liquid-crystal display containing

two outer plates which, together with a frame, form a cell,

a nematic liquid-crystal mixture of positive dielectric anisotropy whichis present in the cell,

electrode layers with alignment layers on the insides of the outerplates,

a pretilt angle between the longitudinal axis of the molecules at thesurface of the outer plates and the outer plates of from about 0 degreeto 30 degrees, and

a twist angle of the liquid-crystal mixture in the cell from alignmentlayer to alignment layer with a value of between 22.5° and 600°,

the nematic liquid-crystal mixture comprises

a) 20-90% by weight of a liquid-crystalline component A consisting ofone or more compounds having a dielectric anisotropy of greater than+1.5;

b) 10-65% by weight of a liquid-crystalline component B consisting ofone or more compounds having a dielectric anisotropy of between -1.5 and+1.5;

c) 0-20% by weight of a liquid-crystalline component C consisting of oneor more compounds having a dielectric anisotropy of below -1.5, and

d) if desired, an optically active component D in such an amount thatthe ratio between the layer thickness (separation of the outer plates)and the natural pitch of the resultant chiral nematic liquid-crystalmixture is from about 0.2 to 1.3,

characterized in that component A comprises at least one compound of theformula IA ##STR5## in which R^(a) is an alkyl group having 1 to 12carbon atoms, in which, in addition, one or two non-adjacent CH₂ groupsmay be replaced by --O--, --CH=CH--, --CO--, --OCO-- or --COO--,

L is H or F, and

r is 0 or 1,

and component B comprises at least one compound of the formula IB##STR6## in which R^(b) and R^(c) are each, independently of oneanother, an alkenyl group having 2 to 7 carbon atoms.

The invention also relates to corresponding liquid-crystal mixtures foruse in STN and TN displays, in particular in high-resolution STNdisplays.

Preferred compounds of the formula IA are, in particular, compounds ofthe subformulae IA1 to IA3: ##STR7##

Preferred compounds of the formula IB are compounds in which R^(b) andR^(c) are 1E-alkenyl or 3E-alkenyl having 2 to 7 carbon atoms, inparticular compounds of the formulae IB1 to IB3: ##STR8## in whichR^(b1) and R^(c1) are each, independently of one another, H, CH₃, C₂ H₅or n-C₃ H₇

Particular preference is given to liquid-crystal displays according tothe invention in which component B comprises at least two compoundsselected from the formulae IB1 and/or IB2 in which R^(b1) and R^(c1)each have the same definition.

Component A preferably comprises, in addition to the compounds of theformula IA, compounds of the formulae II and/or III ##STR9## in which Ris an alkyl group having 1 to 12 carbon atoms, in which, in addition,one or two non-adjacent CH₂ groups may be replaced by --O--, --CH═CH--,--CO--, --OCO-- or --COO--, in particular a trans-alkenyl group having 2to 7 carbon atoms, ##STR10## are each, independently of one another,##STR11## L¹⁻⁶ are each, independently of one another, H or F, Z¹ is--COO--, --CH₂ CH₂ -- or a single bond,

Z² is --CH₂ CH₂ --, --COO--, --C.tbd.C-- or a single bond,

Q is --CF₂ --, --CHF--, --OCF₂ --, --OCHF-- or a single bond,

Y is F or Cl

a is 1 or 2, and

b is 0 or 1.

Preferred compounds of the formula II conform to the subformulae IIa toIId: ##STR12## in which R, L¹, L² and L⁵ are as defined above.

Further preferred compounds of component A conform to the sub-formulaIIla-IIIt or formula 3a-3g: ##STR13##

In addition to one or more compounds of the formula IA and IB, preferredmixtures comprise one, two, three, or more compounds of the formulaeIIa, IIb, IIc, IId, IIIb, IIId, IIIf, IIIh, IIIi, 3b or IIIs, preferablyone or more compounds of the formula IIIb, IIId or IIIh, and one to fourcompounds of the formulae IA and IB and one to three compounds of theformulae IIa and/or IIb.

Particular preference is given to mixtures which comprise one or morecompounds of the formulae IIIb1 ##STR14## in which R_(d) is as definedfor R^(b).

In these compounds, R_(d) is particularly preferably vinyl, 1E-propenyl,1E-butenyl, 3E-butenyl, 3E-pentenyl, in particular vinyl.

The individual compounds, for example, of the formulae II and III, andtheir subformulae, and the other compounds which can be used in the TNliquid-crystal displays and SLCDs according to the invention are eitherknown or can be prepared analogously to the known compounds.

In a particularly preferred embodiment, component A additionallycomprises compounds of the formulae AI to AV: ##STR15## in which R is analkyl group having 1 to 12 carbon atoms, in which, in addition, one ortwo non-adjacent CH₂ groups may also be replaced by --O--, --CH═CH--,--CO--, --OCO-- or --COO--, in particular a trans-alkenyl group having 2to 7 carbon atoms, ##STR16## L⁵ and L⁶ are each, independently of oneanother, H or F, Z³ is ##STR17## --CH₂ CH₂ --, --CO--O--, --O--CO-- or asingle bond, and ##STR18##

The mixtures preferably comprise from 5 to 50% of compounds of theformula AI. Preference is given to compounds of the formula AI in whichZ³ is --CH₂ CH₂ --, --COO-- or a single bond, in particular compounds ofthe formulae IIa1, IIb1 and IIb2: ##STR19##

Component A preferably comprises one or more compounds of the formulaeIIb1.

The mixtures according to the invention preferably comprise one or morepolar compounds having a high clearing point selected from the groupconsisting of the compounds 2e to 2i: ##STR20##

In the compounds 2e to 2i the 1,4-phenylene rings can also be laterallysubstituted by one or two fluorine atoms. Preferred compounds of thistype are the compounds of the formulae 2e1, 2e2, 2e3 and 2i1: ##STR21##

In the mixtures according to the invention, the proportion of compounds2e to 2i is preferably from about 2 to 25%. Preferred liquid-crystalmixtures comprise one or more compounds from component B, preferably 10to 40%. The compounds from component B are preferably distinguished bothby their low rotational viscosity (γ₁) values of <150 mPa.s and by theirhigh clearing point (>120° C.).

Component B preferably, in addition to one or more compounds of theformula IB, comprises one or more compounds selected from the groupconsisting of the compounds of the formulae IV1 to IV9: ##STR22## inwhich R¹ and R² are as defined for R.

In a particularly preferred embodiment, the mixture according to theinvention comprises at least one compound of the formula IB and at leastone compound of the formula IV2.

Component B additionally comprises one or more compounds selected fromthe group consisting of the compounds of the formulae IV10 to IV24:##STR23## in which R¹ and R² are as defined for R, and the 1,4-phenylenegroups in IV10 to IV19, IV23 and IV24 may each, independently of oneanother, also be monosubstituted or polysubstituted by fluorine.

Particular preference is given to mixtures comprising one or morecompounds of the following formulae: ##STR24## in which R^(e) is asdefined for R^(b), and R^(e1) is straight-chain alkyl having 1 to 4carbon atoms.

In these compounds, R^(e) is particularly preferably vinyl, 1E-propenyl,1-butenyl, 2E-butenyl or 2E-pentenyl. R^(e1) is particularly preferablymethyl, ethyl or propyl, in particular methyl or ethyl.

Component B additionally, in addition to one or more compounds offormula Ib, comprises one or more compounds selected from the groupconsisting of the compounds of the formulae IV25 to IV30: ##STR25## inwhich R¹ and R² are as defined for R, and the 1,4-phenylene groups inIV25 to IV30 may also each, independently of one another, bemonosubstituted or polysubstituted by fluorine.

The term "alkenyl" in the definition of R^(b) to R^(e) coversstraight-chain and branched alkenyl groups having 2-7 carbon atoms, inparticular the straight-chain groups. Particularly preferred alkenylgroups are C₂ -C₇ -1E-alkenyl, C₄ -C₇ -3E-alkenyl, C₅ -C₇ -4-alkenyl, C₆-C₇ -5-alkenyl, and C₇ -6-alkenyl, in particular C₂ -C₇ -1E-alkenyl, C₄-C₇ -3E-alkenyl and C₅ -C₇ -4-alkenyl.

Examples of preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl,1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl,3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl,4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groups having up to 5carbon atoms are generally preferred.

Component B optionally comprises one or more compounds selected from thegroup consisting of the compounds of the formulae IV31 and IV32:##STR26## in which C_(r) H_(2r+1) is a straight-chain alkyl group havingup to 9 carbon atoms.

Besides components A, B and C, the liquid-crystal mixture according tothe invention additionally comprises one or more compounds selected fromthe group ##STR27## in which R¹ and R² are as defined for R.

Preferred liquid-crystal mixtures comprise at least one componentselected from the group consisting of the following compounds: ##STR28##in which Hal is F or Cl, L is H or F, and R and R¹ are as defined above.

The liquid-crystal mixtures optionally comprise an optically activecomponent C in such an amount that the ratio between the layer thickness(separation of the outer plates) and the natural pitch of the chiralnematic liquid-crystal mixture is greater than 0.2. For the component, amultiplicity of chiral dopes, some commercially available, are availableto the person skilled in the art, for example such as cholesterylnonanoate, S-811 from Merck KGaA, Darmstadt, FRG, and CB 15 (BDH, Poole,UK). The choice of dopes is not crucial per se.

The liquid-crystal mixture according to the invention preferablycomprises one or more compounds selected from Group B1 consisting ofcompounds of the formulae B1I to B1IV: ##STR29## in which R¹ and R² areeach, independently of one another, as defined for R,

Z is --CH₂ CH₂ --, --CO--O--, --O--CO-- or a single bond, and, ##STR30##and/or at least one compound selected from Group B2 consisting ofcompounds of the formulae B1V to B1VII: ##STR31## in which R is asdefined above,

Z⁰ is --CH₂ CH₂ -- or a single bond,

Q⁰ is ##STR32## where r is 1-9, X is CN or F,

L¹ is H or F,

and/or at least one compound selected from Group B3 consisting ofcompounds of the formulae B1VIII, B1IX and B1X: ##STR33## in which R¹and R², independently of one another, are as defined for R,

Y is F or Cl, and ##STR34##

In a particularly preferred embodiment, the mixtures according to theinvention comprise from about 5 to 35%, in particular from 10 to 20%, ofliquid-crystalline tolan compounds. This enables smaller layerthicknesses (about 5-6 μm) to be used, significantly shortening theresponse times. Particular preference is given to mixtures comprisingone or more compounds selected from Group T consisting of the compoundsof the formulae T1 to T3: ##STR35## in which the individual radicalshave the following meaning ##STR36## t is 0 or 1,

L¹, L², L⁵ and L⁶ are each, independently of one another, H or F,

Q is --CF₂ --, --CHF--, --OCF₂ --, --OCHF-- or a single bond,

Y is F or Cl,

Z⁰ is --CO--O--, --CH₂ CH₂ -- or a single bond, and

R¹ and R² are each, independently of one another, as defined for R,

R⁷ is --C_(x) H_(2x+1), --OC_(x) H_(2x+1), ##STR37## x is an integerfrom 1 to 15, and X' is F, Cl or OCF₃.

The proportion of compounds from the group T is preferably from 5 to30%, in particular from 5 to 20%.

The liquid-crystalline tolan compounds present in the mixtures accordingto the invention can, depending on their dielectric anisotropy values,be assigned to one of components A, B and C according to the limitvalues mentioned for these components.

Component B preferably comprises one or more compounds of the formulae Xto XIII: ##STR38## in which R¹ and R² are each, independently of oneanother, as defined for R, and R¹ is preferably alkyl having 1 to 4carbon atoms, in particular 1 to 2 carbon atoms, and R² is preferablyalkoxy having 1 to 4 carbon atoms, in particular 1 to 2 carbon atoms.

The proportion of compounds from group B1 is preferably from 10 to 50%,in particular from 15 to 40%. Compounds of the formula B1III and B1IVare preferred.

Particularly preferred compounds of the formula B1III are those of thefollowing subformulae B1IIIa and B1IIIb ##STR39## in which R^(3') is CH₃--(CH₂)_(o) --, CH₃ --(CH₂)_(o) --O--, CH₃ --(CH₂)_(p) --,trans-H-(CH₂)_(q) --CH═CH--(CH₂ CH₂)_(b) --CH₂ O-- or trans-H-(CH₂)_(q)--CH═CH--(CH₂ CH₂)_(b) --; CH₃ --(CH₂)_(o) --O--CH₂ --,

R^(4') is CH₃ --(CH₂)_(p) --,

o is 0, 1, 2, 3 or 4,

q is 0, 1, 2 or 3,

b is 0 or 1, and

p is 1, 2, 3 or 4.

Particular preference is given to compounds of the subformula B1IIIa inwhich R^(3') is trans-H-(CH₂)_(q) --CH═CH-- and the formula B1III inwhich one of the radicals R¹ or R² is O--(CH₂)_(o) --CH₃ or CH₂--O--(CH₂)_(o) --CH₃.

Preference is furthermore given to the compounds of the subformula##STR40## in which R^(3') and R^(4') are each, independently of oneanother, as defined above.

The proportion of compounds of the abovementioned sub-formulae offormula B1III is preferable from about 5 to 45%, particularly preferablyfrom about 10% to 35%. Particularly preferred compounds of the formulaB1IV are those of the following subformula ##STR41## in which R* is CH₃--(CH₂)_(o) --O-- or trans-H-(CH)_(q) --CH═CH--((H₂ CH₂)_(b) --CH₂ O--,and

R^(2') is CH₃ --(CH₂)_(p) --, where

o is 0, 1, 2, 3 or 4,

q is 0, 1, 2 or 3,

b is 0 or 1, and

p is 1, 2, 3 or 4.

The proportion of these compounds or of compounds of the formula BIV ispreferably from about 5 to 40%, particularly preferably from about 10 to35%.

In a particularly preferred embodiment, the mixtures simultaneouslycomprise compounds of the formulae B1III and B1IV, where the totalproportion of components from group B1 remains observed.

If compounds of the formulae B1I and/or B1III are present, R¹ and R² arepreferably each, independently of one another, n-alkyl having 1 to 7carbon atoms or (trans)-n-alkenyl having 3 to 7 carbon atoms. Z ispreferably a single bond.

Preference is furthermore given to mixtures according to the inventionwhich comprise one or more compounds of the formula B1IV in which##STR42## and R¹ and R² have one of the preferred meanings given above,particularly preferably n-alkyl having 1 to 7 carbon atoms.

In all cases, the total proportion of components from group B1 remainsobserved.

The proportion of compounds from group B2 is preferably from about 5 to45%, in particular from 5 to 20%. The proportion (preferred ranges) forB1V to B1VII is as follows:

B1V: from about 5 to 30%, preferably from about 5 to 15% Sum of B1VI

and B1VII: from about 5 to 25%, preferably from about 10 to 20%.

Preferred compounds from group B2 are shown below: ##STR43## R¹ ispreferably n-alkyl having 1 to 7 carbon atoms or (trans)-n-alkenylhaving 2 to 7 carbon atoms. Z⁰ is preferably a single bond. R'preferably has the preferred meaning given above for R or is fluorine.L¹ is preferably fluorine and r is 1-9.

The mixtures according to the invention preferably comprise one or morecompounds selected from the group consisting of B1V3, B1VIl and B1VII1in a total proportion of from about 5 to 35%.

In a particularly preferred embodiment, the mixtures according to theinvention, in addition to B1V3, B1VIl and B1VIIl (L¹ =F), comprisefurther terminally fluorinated compounds selected, for example, from thegroup consisting of ##STR44## and/or polar heterocyclic compoundsselected from the group consisting of ##STR45## in which R¹ ispreferably n-alkyl having 1 to 7 carbon atoms or (trans)-n-alkenylhaving 3 to 7 carbon atoms, a is 1 or 2, b is 0 or 1, X⁰ is F, Cl, CF₃,--OCF₃ or --OCHF₂, and L and L¹ are H or F.

The total proportion of all terminally fluorinated compounds ispreferably from about 5 to 65%, in particular from about 15 to 40%.

The proportion of compounds from group B3 is preferably from about 5 to30%, particularly preferably from about 10 to 20%. R¹ is preferablyn-alkyl or n-alkoxy, in each case having 1 to 9 carbon atoms.

However, it is also possible to use analogous compounds containingalkenyl or alkenyloxy groups. Compounds of the formula B1VIII arepreferred.

The mixtures according to the invention comprise compounds of theformulae IA and IB and preferably compounds from at least one of groupsB1, B2 and B3. They preferably comprise one or more compounds from groupB1 and one or more compounds from group B2 and/or B3.

The proportion of compounds of component C is preferably from 0 to 20%,in particular from 0 to 10%.

In a particularly preferred embodiment, the mixtures according to theinvention preferably comprise from about 5 to 20% of one or morecompounds having a dielectric anisotropy of below -2 (component C). Suchcompounds are known, for example derivatives of 2,3-dicyanohydroquinonesor cyclohexane derivatives containing the structural unit ##STR46## asdefined in DE-A 32 32 707 or DE-A 34 07 013.

However, preference is given to compounds containing the structural unit2,3-difluoro-1,4-phenylene, for example compounds as described in DE-A38 07 801, DE 38 07 861, DE 38 07 863, DE 38 07 864 or DE 38 07 908.Particular preference is given to tolans containing this structuralunit, as described in International Patent Application PCT/DE 88/00133,in particular those of the formulae ##STR47## in which R⁵ and R⁶ areeach, independently of one another, preferably n-alkyl having 1 to 7carbon atoms or n-alkenyl having 3 to 7 carbon atoms, and Z⁰ is--COO--CH₂ CH₂ -- or a single bond.

Particular preference is given to phenylcyclohexyl carboxylates of theformulae ##STR48##

Component C preferably comprises one or more compounds selected from thegroup consisting of V to IX: ##STR49## in which R¹ and R² are as definedfor R, and b is 0 or 1.

In particular, component C results in increased steepness of thecharacteristic line.

Component B preferably further comprises one or more compounds selectedfrom the group consisting of Xa to XIIa: ##STR50## in which Alkyl andAlkoxy are a straight-chain alkyl or alkoxy radical having 1 to 7 carbonatoms.

In further particularly preferred embodiments,

Component C comprises one or more compounds containing a1-cyano-trans-1,4-cyclohexyl group or a 2,3-difluoro-1,4-phenylenegroup;

at least two compounds of the formulae AIII or AV;

compounds of the formulae AIII and AV;

at least one compound from the group consisting of: ##STR51## in whichAlkyl is a straight-chain alkyl or alkenyl radical having 2 to 7 carbonatoms, and L is H or F;

one or more compounds in which R is a trans-alkenyl group or atrans-alkenyloxy group;

one or more compounds selected from the following group: ##STR52## inwhich R¹ and R² have the preferred meanings given under compounds ofcomponent B. The 1,4-phenylene groups in the abovementioned compoundscan also be substituted by fluorine. The proportion of these compoundsin the liquid-crystal mixtures is from 0 to 25%, preferably from 5 to15%.

In further preferred embodiments, the mixtures comprise

one or more, in particular 1, 2, 3 or 4, compounds selected from thecompounds of the formulae IIIb, IIId, IIIf, IIIh and IIIi;

at least two compounds selected from the compounds of the formulae IIa1,IIb1 and IIb2;

one or more compounds of the formula B1IV;

one or more compounds of the formula T1 or T2;

one or more compounds of the formulae ##STR53## in which R is as definedunder the formula III.

In a preferred embodiment, the liquid-crystalline media according to theinvention comprise 3, 4, 5 or 6 compounds of the formula IA and/or IB;the content of these compounds is generally from 10 to 60% by weight,preferably from 15 to 50% by weight, based on the overall mixture.

Media comprising compounds of the formula IB in which R^(b) is H areparticularly preferred.

In particular when used in SLCDs and TN displays having high layerthicknesses, the mixtures according to the invention are distinguishedby very low overall response times (=t_(on) +t_(off)).

Low overall response times are an important criterion, in particular, inSLCDs for use as displays in laptops in order to be able to displaycursor movements without interference.

The liquid-crystal mixtures used in the STN and TN cells according tothe invention are dielectrically positive with Δε≧1. Particularpreference is given to liquid-crystal mixtures where Δε≧3 and veryparticularly to those where Δε≧5.

The liquid-crystal mixtures according to the invention have favorablevalues for the threshold voltage V_(10/0/20) and for the rotationalviscosity γ₁. If the value for the optical path difference d.Δn isspecified, the value for the layer thickness d is determined by theoptical anisotropy Δn. In particular at relatively high values for d.Δn,the use of liquid-crystal mixtures according to the invention having arelatively high value for the optical anisotropy is generally preferredsince the value for d can then be chosen to be relatively small, whichresults in more favorable values for the response times. However,liquid-crystal displays according to the invention which containliquid-crystal mixtures according to the invention having relativelysmall values for Δn are also characterized by advantageous values forthe response times. The liquid-crystal mixtures according to theinvention are furthermore characterized by advantageous values for thesteepness of the electrooptical characteristic line and can be operatedat high multiplex rates. In addition, the liquid-crystal mixturesaccording to the invention have high stability and favorable values forthe electrical resistance and the frequency dependence of the thresholdvoltage. The liquid-crystal displays according to the invention have abroad operating temperature range and good angle dependence of thecontrast.

The construction of the liquid-crystal display elements according to theinvention from polarizers, electrode baseplates and electrodes with asurface treatment such that the preferential alignment (director) of theliquid-crystal molecules in each case adjacent thereto is usuallytwisted by a value of from 160° to 720° from one electrode to the next,corresponds to the structure which is conventional for display elementsof this type. The term conventional structure here is broadly drawn andalso includes all derivatives and modifications of the TN and STN cell,in particular also matrix display elements, and display elements whichcontain additional magnets. The surface tilt angle at the two outerplates may be identical or different. Identical tilt angles arepreferred. Preferred TN displays have pretilt angles between thelongitudinal axis of the molecules at the surface of the outer platesand the outer plates of from 0° to 7°, preferably from 0.01° to 5°, inparticular from 0.1 to 2°. In STN displays, the pretilt angle is from 1°to 30°, preferably from 1° to 12°, in particular from 3° to 8°.

The twist angle of the TN mixture in the cell has a value of between22.5° and 170°, preferably between 45° and 130°, in particular between80° and 115°. The twist angle of the STN mixture in the display fromalignment layer to alignment layer has a value of between 100° and 600°,preferably between 170° and 300°, in particular between 180° and 270°.

The liquid-crystal mixtures which can be used according to the inventionare prepared in a manner which is known per se. In general, the desiredamount of the components used in a lesser amount is dissolved in thecomponents making up the principal constituent, expediently at elevatedtemperature. It is also possible to mix solutions of the components inan organic solvent, for example in acetone, chloroform or methanol, and,after mixing, to remove the solvent again, for example by distillation.

The dielectrics may also contain further additives which are known to aperson skilled in the art and are described in the literature. Forexample, 0-15% of pleochroic dyes may be added.

In the foregoing and in the following examples, all temperatures are setforth uncorrected in degrees Celsius; and, unless otherwise indicated,all parts and percentages are by weight.

The entire disclosure of all applications, patents and publications,cited above and below, and of corresponding German Application No. 19707 956.3, filed Feb. 27, 1997 is hereby incorporated by reference.

The examples below are intended to illustrate the invention withoutrepresenting a limitation.

The following abbreviations are used:

    ______________________________________                                        S-N        smectic-nematic phase transition temperature,                      N-I        nematic-isotropic phase transition tempera-                                   ture,                                                              c.p.       clearing point,                                                    visc.      rotational viscosity (mPa.s)                                       t.sub.on   time from switching on until 90% of the                                       maximum contrast is achieved,                                      t.sub.off  time from switching off until 10% of the                                      maximum contrast is achieved,                                      V.sub.90 /V.sub.10                                                                       steepness,                                                         t.sub.ave  t.sub.on  + t.sub.off  (average response time).                                    2                                                             ______________________________________                                    

The SLCD is operated in multiplex mode (multiplex ratio 1:240, bias1:16, operating voltage between 20 and 30 volts, so that t_(on)=t_(off)).

Above and below, all temperatures are indicated in °C. The percentagesare per cent by weight. The values for the response times andviscosities relate to 20° C.

In the present application and in the examples below, the structures ofthe liquid-crystal compounds are indicated by acronyms, thetransformation into chemical formulae taking place in accordance withtables A and B below. All radicals C_(n) H_(2n+1) and C_(m) H_(2m+1) arestraight-chain alkyl radicals having n and m carbon atoms respectively.The alkenyl radicals have the trans-configuration. The coding in Table Bis self-evident. In Table A, only the acronym for the parent strictureis given. In individual cases, the acronym for the parent structure isfollowed, separated by a dash, by a code for the substituents R¹, R²,L¹, L² and L³ :

    __________________________________________________________________________    Code for R.sup.1, R.sup.2                                                     L.sup.1, L.sup.2, L.sup.3                                                              R.sup.1    R.sup.2        L.sup.1 L.sup.2 L.sup.3                    __________________________________________________________________________    nm       C.sub.m H.sub.2m+1                                                                       C.sub.n H.sub.2n+1                                                                           H H H                                      nOm      OC.sub.m H.sub.2m+1                                                                      C.sub.n H.sub.2n+1                                                                           H H H                                      nO.m     C.sub.m H.sub.2m+1                                                                       OC.sub.n H.sub.2n+1                                                                          H H H                                      n        CN         C.sub.n H.sub.2n+1                                                                           H H H                                      nN.F     CN         C.sub.n H.sub.2n+1                                                                           H H F                                      nF       F          C.sub.n H.sub.2n+1                                                                           H H H                                      nOF      F          OC.sub.n H.sub.2n+1                                                                          H H H                                      nCl      Cl         C.sub.n H.sub.2n+1                                                                           H H H                                      nF.F     F          C.sub.n H.sub.2n+1                                                                           H H F                                      nmF      C.sub.m 2.sub.2m+1                                                                       C.sub.n H.sub.2n+1                                                                           H F H                                      nCF.sub.3                                                                              CF.sub.3   C.sub.n H.sub.2n+1                                                                           H H H                                      nOCF.sub.3                                                                             OCF.sub.3  C.sub.n H.sub.2n+1                                                                           H H H                                      nOCF.sub.2                                                                             OCHF.sub.2 C.sub.n H.sub.2n+1                                                                           H H H                                      nS       NCS        C.sub.n H.sub.2n+1                                                                           H H H                                      rVsN     CN         C.sub.r H.sub.2r+1 --CH═CH--C.sub.s H.sub.2s                                             H H H                                      rEsN     CN         C.sub.r H.sub.2r+1 --O--C.sub.2 H.sub.2s --                                                  H H H                                      nNF      CN         C.sub.n H.sub.2n+1                                                                           H F H                                      nAm      COOC.sub.m H.sub.2m+1                                                                    C.sub.n H.sub.2n+1                                                                           H H H                                      nF.Cl    Cl         C.sub.n H.sub.2n+1                                                                           H H F                                      n-Vm     --CH═CH--C.sub.m H.sub.2m+1                                                          C.sub.n H.sub.2n+1                                                                           H H H                                      nV--Vm   --CH═CH--C.sub.m H.sub.2m+1                                                          C.sub.n H.sub.2n+1 --CH═CH--                                                             H H H                                      nV-m     --CmH.sub.2m+1                                                                           C.sub.n H.sub.2n+1 --CH═CH--                                                             H H H                                      nV--Om   --OC.sub.m H.sub.2m+1                                                                    C.sub.n H.sub.2n+1 --CH═CH--                                                             H H H                                               n          =                                                         nV--N    C.sub.n H.sub.2n+1 --CH═CH--                                                         --CN           H H H                                      nV--F    C.sub.n H.sub.2n+1 --CH═CH--                                                         F              H H H                                      nV--F.F  C.sub.n H.sub.2n+1 --CH═CH--                                                         F              H H F                                      n-2Vm    C.sub.n H.sub.2n+1                                                                       C.sub.m H.sub.2m+1 --CH═CH--CH.sub.2 CH.sub.2                                            H H H                                      __________________________________________________________________________

The TN and STN displays preferably contain liquid-crystalline mixturescomposed of one or more compounds from Tables A and B.

                  TABLE A                                                         ______________________________________                                        (L.sup.1, L.sup.2, L.sup.3 = H or F)                                          ______________________________________                                         ##STR54##                                                                     ##STR55##                                                                     ##STR56##                                                                     ##STR57##                                                                     ##STR58##                                                                     ##STR59##                                                                     ##STR60##                                                                     ##STR61##                                                                     ##STR62##                                                                     ##STR63##                                                                     ##STR64##                                                                     ##STR65##                                                                     ##STR66##                                                                     ##STR67##                                                                    ______________________________________                                    

                  TABLE B                                                         ______________________________________                                         ##STR68##                                                                     ##STR69##                                                                     ##STR70##                                                                     ##STR71##                                                                     ##STR72##                                                                     ##STR73##                                                                     ##STR74##                                                                     ##STR75##                                                                     ##STR76##                                                                     ##STR77##                                                                     ##STR78##                                                                     ##STR79##                                                                     ##STR80##                                                                     ##STR81##                                                                     ##STR82##                                                                     ##STR83##                                                                     ##STR84##                                                                    ______________________________________                                    

The examples below are intended to illustrate the invention withoutrepresenting a limitation. Above and below, percentages are per cent byweight. All temperatures are given in degrees celsius. m.p. denotesmelting point, c.p.=clearing point. Furthermore, C=crystalline state,N=nematic phase, S=smectic phase and I=isotropic phase. The numbersbetween these symbols are the transition temperatures. An denotesoptical anisotropy (589 nm, 20° C.), V₁₀ denotes the threshold voltageand V₉₀ /V₁₀ denotes the steepness of the characteristic line of theliquid-crystal display according to the invention. Unless statedotherwise, the response time is the mean of the switch-on and switch-offtimes.

EXAMPLE 1

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     13.00%      Clearing point:                                                                            93.5° C                             K6        7.00%       .increment.n:                                                                              0.1211                                     ME2N.F    3.00%       n.sub.0 :    1.4995                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.20 V                                     CBC-33    4.00%       V.sub.90 /V.sub.10 :                                                                       1.03                                       CBC-33F   4.00%       Response time:                                                                             292 ms                                     CC-V-V    20.00%                                                              CCP-V-1   14.00%                                                              CCP-V2-1  15.00%                                                              CPP-1V2-2 5.00%                                                               CCG-V-F   9.00%                                                               ______________________________________                                    

EXAMPLE 2

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     13.00%      Clearing point:                                                                            114° C                              K6        7.00%       .increment.n:                                                                              0.1306                                     ME2N.F    3.00%       n.sub.0 :    1.4990                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.47 V                                     CBC-33    4.00%       V.sub.90 /V.sub.10 :                                                                       1.019                                      CBC-33F   4.00%       Response time:                                                                             303 ms                                     CC-1V-V1  20.00%                                                              CCP-V-1   14.00%                                                              CCP-V2-1  15.00%                                                              CPP-1V2-2 5.00%                                                               CCG-V-F   9.00%                                                               ______________________________________                                    

EXAMPLE 3

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     13.00%      Clearing point:                                                                            110° C                              K6        7.00%       .increment.n:                                                                              0.1259                                     ME2N.F    3.00%       n.sub.0 :    1.4986                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.33 V                                     CBC-33    4.00%       V.sub.90 /V.sub.10 :                                                                       1.041                                      CBC-33F   4.00%       Response time:                                                                             298 ms                                     CC-2V-V2  20.00%                                                              CCP-V-1   14.00%                                                              CCP-V2-1  15.00%                                                              CPP-1V2-2 5.00%                                                               CCG-V-F   9.00%                                                               ______________________________________                                    

EXAMPLE 4

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     13.00%      Clearing point:                                                                            99° C                               K6        7.00%       .increment.n:                                                                              0.1230                                     ME2N.F    3.00%       n.sub.0 :    1.4181                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.39 V                                     CBC-33    4.00%       V.sub.90 /V.sub.10 :                                                                       1.026                                      CBC-33F   4.00%       Response time:                                                                             254 ms                                     CC-V-V1   29.00%                                                              CCP-V-1   14.00%                                                              CCP-V2-1  15.00%                                                              CPP-1V2-2 5.00%                                                               ______________________________________                                    

EXAMPLE 5

    ______________________________________                                        An STM mixture comprising                                                     ______________________________________                                        PCH-3     15.00%      Clearing point:                                                                            94° C                               K6        8.00%       .increment.n:                                                                              0.1254                                     ME2N.F    3.00%       n.sub.0 :    1.4958                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.26 V                                     CC-2V-V2  30.00%      V.sub.90 /V.sub.10 :                                                                       1.051                                      CCP-V-1   15.00%      Response time:                                                                             230 ms                                     CCP-V2-1  14.00%                                                              CPP-1V2-2 5.00%                                                               CPTP-302  4.00%                                                               ______________________________________                                    

EXAMPLE 6

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     12.00%      Clearing point:                                                                            95.5° C                             K6        10.00%      .increment.n:                                                                              0.1259                                     ME2N.F    3.00%       n.sub.0 :    1.4991                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.28 V                                     CBC-33    4.00%       V.sub.90 /V.sub.10 :                                                                       1.025                                      CBC-33F   4.00%       Response time:                                                                             244 ms                                     CC-V-V1   29.00%                                                              CCP-V-1   12.00%                                                              CCP-V2-1  15.00%                                                              CCP-1V2-2 4.00%                                                               ______________________________________                                    

EXAMPLE 7

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     13.00%     Clearing point:                                                                            108.5° C                             K6        7.00%      .increment.n:                                                                              0.1258                                      ME2N.F    3.00%      n.sub.0 :    1.4991                                      ME3N.F    2.00%      Twist:       240°                                 ME4N.F    4.00%      V.sub.10 :   2.35 V                                      CBC-33    4.00%      V.sub.90 /V.sub.10 :                                                                       1.038                                       CBC-33F   4.00%      Response time:                                                                             294 ms                                      CC-V2-V2  20.00%                                                              CCP-V-1   14.00%                                                              CCP-V2-1  15.00%                                                              CPP-1V2-2 5.00%                                                               CCG-V-F   9.00%                                                               ______________________________________                                    

EXAMPLE 8

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     11.00%      Clearing point:                                                                            100° C                              K6        9.00%       .increment.n:                                                                              0.1287                                     ME2N.F    3.00%       n.sub.0 :    1.5006                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.31 V                                     CBC-33    3.00%       V.sub.90 /V.sub.10 :                                                                       1.029                                      CBC-33F   3.00%       Response time:                                                                             245 ms                                     CC-V-V1   20.00%                                                              CCP-V-1   15.00%                                                              CCP-V2-1  16.00%                                                              CPP-1V2-2 10.00%                                                              CC-5-V    4.00%                                                               ______________________________________                                    

EXAMPLE 9

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     11.00%      Clearing point:                                                                            99° C                               K6        9.00%       .increment.n:                                                                              0.1267                                     ME2N.F    3.00%       n.sub.0 :    1.5005                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.29 V                                     CBC-33    3.00%       V.sub.90 /V.sub.10 :                                                                       1.042                                      CBC-33F   3.00%       Response time:                                                                             254 ms                                     CC-2V-V2  10.00%                                                              CC-V-V    10.00%                                                              CCP-V-1   15.00%                                                              CCP-V2-1  16.00%                                                              CPP-1V2-2 10.00%                                                              CC-5-V    4.00%                                                               ______________________________________                                    

EXAMPLE 10

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     11.00%      Clearing point:                                                                            101° C                              K6        9.00%       .increment.n:                                                                              0.1303                                     ME2N.F    3.00%       n.sub.0 :    1.5001                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.38 V                                     CBC-33    3.00%       V.sub.90 /V.sub.10 :                                                                       1.035                                      CBC-33F   3.00%       Response time:                                                                             230 ms                                     CC-1V-V1  10.00%                                                              CC-V-V    10.00%                                                              CCP-V-1   15.00%                                                              CCP-V2-1  16.00%                                                              CPP-1V2-2 10.00%                                                              CC-5-V    4.00%                                                               ______________________________________                                    

EXAMPLE 11

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     10.00%      Clearing point:                                                                            101° C                              K6        8.00%       .increment.n:                                                                              0.1306                                     ME2N.F    4.00%       n.sub.0 :    1.4994                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.28 V                                     CBC-33    3.00%       V.sub.90 /V.sub.10 :                                                                       1.034                                      CBC-33F   4.00%       Response time:                                                                             230 ms                                     CC-2V-V2  10.00%                                                              CC-V-V    16.00%                                                              CCP-V-1   15.00%                                                              CCP-V2-1  16.00%                                                              CPTP-303  4.00%                                                               CPTP-302  4.00%                                                               ______________________________________                                    

EXAMPLE 12

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     10.00%      Clearing point:                                                                            96° C                               K6        10.00%      .increment.n:                                                                              0.1381                                     ME2N.F    4.00%       n.sub.0 :    1.5015                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    4.00%       V.sub.10 :   2.17 V                                     CBC-33    3.00%       V.sub.90 /V.sub.10 :                                                                       1.044                                      CBC-33F   4.00%       Response time:                                                                             195 ms                                     CC-2V-V2  10.00%                                                              CC-V-V    13.00%                                                              CCP-V-1   15.00%                                                              CCP-V2-1  16.00%                                                              CPTP-303  5.00%                                                               PTP-102   4.00%                                                               ______________________________________                                    

EXAMPLE 13

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     10.00%      Clearing point:                                                                            102° C                              K6        7.50%       .increment.n:                                                                              0.1315                                     ME2N.F    4.00%       n.sub.0 :    1.4985                                     ME3N.F    2.00%       Twist:       240° C                              ME4N.F    4.00%       V.sub.10 :   2.37 V                                     CBC-33    3.00%       V.sub.90 /V.sub.10 :                                                                       1.028                                      CBC-33F   3.50%       Response time:                                                                             235 ms                                     CC-1V-V1  10.00%                                                              CC-V-V    17.00%                                                              CCP-V-1   15.00%                                                              CCP-V2-1  16.00%                                                              CPTP-303  4.00%                                                               CPTP-302  4.00%                                                               ______________________________________                                    

EXAMPLE 14

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     11.00%      Clearing point:                                                                            99° C                               K6        10.00%      Δn:    0.1408                                     ME2N.F    4.00%       n.sub.o :    1.5016                                     ME3N.F    2.00%       Twist:       240°                                ME4N.F    3.00%       V.sub.10 :   2.30 V                                     CBC-33    4.00%       V.sub.90 /V.sub.10 :                                                                       1.033                                      CBC-33F   3.00%       Response time:                                                                             197 ms                                     CC-1V-V1  10.00%                                                              CC-V-V    13.00%                                                              CCP-V-1   15.00%                                                              CCP-V2-1  16.00%                                                              CPTP-303  5.00%                                                               PTP-102   4.00%                                                               ______________________________________                                    

EXAMPLE 15

    ______________________________________                                        An STN mixture comprising                                                     ______________________________________                                        PCH-3     15.00%      Clearing point:                                                                            99° C                               ME2N.F    2.00%       .increment.n:                                                                              0.1449                                     ME3N.F    3.00%       Twist:       240°                                ME4N.F    7.00%       V.sub.10 :   2.29 V                                     CC-5-V    12.00%      V.sub.90 /V.sub.10 :                                                                       1.041                                      CC-1V-V1  10.00%      Response time:                                                                             203 ms                                     CCP-V-1   15.00%                                                              CCP-V2-1  16.00%                                                              PTP-102   5.00%                                                               PTP-201   5.00%                                                               CPTP-301  5.00%                                                               CPTP-303  5.00%                                                               ______________________________________                                    

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

What is claimed is:
 1. A liquid-crystal display comprising:two outerplates which, together with a frame, form a cell, a nematicliquid-crystal mixture of positive dielectric anisotropy which ispresent in the cell, electrode layers with alignment layers on theinsides of the outer plates, a pretilt angle between the longitudinalaxis of the molecules at the surface of the outer plates and the outerplates of 0-30 degrees, and a twist angle of said liquid-crystal mixturein the cell from alignment layer to alignment layer with a value of22.5°-600°;wherein said nematic liquid-crystal mixture comprises: a)20-90% by weight of a liquid-crystalline component A of one or morecompounds having a dielectric anisotropy of greater than +1.5; b) 10-65%by weight of a liquid-crystalline component B of one or more compoundshaving a dielectric anisotropy of -1.5-+1.5; c) 0-20% by weight of aliquid-crystalline component C of one or more compounds having adielectric anisotropy of below -1.5, and d) optionally an opticallyactive component D in an amount whereby the ratio between the separationof the outer plates and the natural pitch of the resultant chiralnematic liquid-crystal mixture is 0.2-1.3;wherein component A comprisesat least one compound of formula IA ##STR85## in which R^(a) is an alkylgroup having 1 to 12 carbon atoms, in which, in addition, one or twonon-adjacent CH₂ groups may be replaced by --O--, --CH═CH--, --CO--,--OCO-- or --COO--, L is H or F, and r is 0 or 1; andwherein component Bcomprises at least one compound of formula IB ##STR86## in which R^(b)and R^(c) are each, independently of one another, an alkenyl grouphaving, 2 to 7 carbon atoms.
 2. A display according to claim 1, whereincomponent A further comprises one or more compounds of formulae II andIII ##STR87## in which R is an alkyl group having 1 to 12 carbon atoms,in which, in addition, one or two non-adjacent CH₂ groups may bereplaced by --O--, --CH═CH--, --CO--, --OCO-- or --COO--, ##STR88## areeach, independently of one another, ##STR89## L¹⁻⁶ are each,independently of one another, H or F, Z¹ is --COO--, --CH₂ CH₂ -- or asingle bond,Z² is --CH₂ CH₂ --, --COO--, --C.tbd.C-- or a single bond, Qis --CF₂ --, --CHF--, --OCF₂, --OCHF-- or a single bond, Y is F or Cl ais 1 or 2, and b is 0 or
 1. 3. A display according to claim 1, whereincomponent A further comprises at least one compound of formulae IIa toIId ##STR90## wherein R is an alkyl group having 1 to 12 carbon atoms,in which, in addition, one or two non-adjacent CH₂ groups may bereplaced by --O--, --CH═CH--, --CO--, --OCO-- or --COO--,L¹ is H or F,L² is H or F, and L⁵ is H or F.
 4. A display according to claim 1,wherein component B further comprises one or more compounds of formulaeIV1 to IV24: ##STR91## in which R¹ and R² are each, independently of oneanother, an alkyl group having 1 to 12 carbon atoms, in which, inaddition, one or two non-adjacent CH₂ groups may be replaced by --O--,--CH═CH--, --CO--, --OCO-- or --COO--.
 5. A display according to claim1, wherein component B further comprises one or more compounds of thefollowing formulae: ##STR92## in which R^(e) is an alkenyl group having2 to 7 carbon atoms, andR^(e1) is straight-chain alkyl having 1 to 4carbon atoms.
 6. A display according to claim 1, wherein component Ccomprises one or more compounds of formulae V to IX ##STR93## in whichR¹ and R² are each, independently of one another, an alkyl group having1 to 12 carbon atoms, in which, in addition, one or two non-adjacent CH₂groups may be replaced by --O--, --CH═CH--, --CO--, --OCO-- or --COO--,andb is 0 or
 1. 7. A display according to claim 1, wherein component Bfurther comprises one or more compounds of formulae Xa to XIIIa:##STR94## in which Alkyl is a straight-chain alkyl having 1 to 7 carbonatoms and alkoxy is an alkoxy having 1 to 7 carbon atoms.
 8. A displayaccording to claim 1, wherein component A further comprises one or morecompounds of formula T3 ##STR95## in which R⁷ is --C_(x) H_(2x+1),--OC_(x) H_(2x+1), ##STR96## x is 1-15, L¹, L², L⁵ and L⁶ are eachindependently of one another, H or F, andX' is F, Cl or OCF₃.
 9. Adisplay according to claim 2, wherein R is a trans-alkenyl group having2-7 carbon atoms.
 10. A display according to claim 3, wherein R is atrans-alkenyl group having 2-7 carbon atoms.
 11. A display according toclaim 4, wherein at least one of R¹ and R² is a trans-alkenyl grouphaving 2-7 carbon atoms.
 12. A display according to claim 6, wherein atleast one of R¹ and R² is a trans-alkenyl group having 2-7 carbon atoms.13. A display according to claim 1, wherein Component C contains one ormore compounds containing a 1-cyano-trans-1,4-cyclohexyl group or a2,3-difluoro-1,4-phenylene group.
 14. A display according to claim 2,wherein said mixture contains one or more compounds in which R istrans-alkenyl or trans-alkenyloxy.
 15. A display according to claim 1,wherein said mixture comprises 3-6 compounds of formula IA and IB, andthe amount of compounds of formulae IA and IB in said mixture is 10-60wt. % based on the overall mixture.
 16. A liquid-crystal mixturecomprising:a) 20-90% by weight of a liquid-crystalline component Aconsisting of one or more compounds having a dielectric anisotropy ofgreater than +1.5; b) 10-65% by weight of a liquid-crystalline componentB consisting of one or more compounds having a dielectric anisotropy ofbetween -1.5 and +1.5; and c) 0-20% by weight of a liquid-crystallinecomponent C consisting of one or more compounds having a dielectricanisotropy of below -1.5;wherein component A comprises at least onecompound of formula IA ##STR97## in which R⁴ is an alkyl group having 1to 12 carbon atoms, in which, in addition, one or two non-adjacent CH₂groups may be replaced by --O--, --CH═CH--, --CO--, --OCO-- or --COO--,L is H or F, and r is 0 or 1; andwherein component B comprises at leastone compound of formula IB ##STR98## in which R^(b) and R^(c) are each,independently of one another, an alkenyl group having 2 to 7 carbonatoms.
 17. A liquid crystal mixture according to claim 16, wherein saidmixture further comprises an optically active component D in an amountwhereby when said liquid crystal mixture is positioned between outerplates of a cell, the ratio between the separation of said outer platesand the natural pitch of the resultant chiral nematic liquid-crystalmixture is 0.2-1.3.